New parameter to select the root view animation effect

Hi Philippe,

I've done a simple modification of the popup ASDepthModal adding an optional parameter in the call to "presentView" that defines the style of the animation of the root view controller. I've updated, too, the demo project adding a new selector to this style. It's a simple modification, but I hope you'll find it useful and you'll integrate it into the main branch.

Best regards,
Ivan Oliver <ivan.oliver@gmail.com>